Neuroscientists at University College London asked people to guess their odds of experiencing bad luck, with and without previous information on the mishaps, and analyzed their brains via fMRI.
[They] asked 19 individuals between the ages of 19 and 27 to estimate their odds of experiencing 80 unfavorable events, such as contracting various diseases or being the victim of a crime. Participants were then told the actual average probability of each before repeating the exercise.
The participants revised most of their estimates the second time around, but 79 percent of those tested paid much more attention when their actual risk was lower than what they had initially guessed. After getting the good news, these subjects rated their risk for these events as significantly lower than they did earlier. In contrast, when they had underestimated their odds of meeting with a particular misfortune, they made less drastic revisions to their guess or none at all—clinging to their earlier belief that they would probably avoid the bad luck.
In other words, we’re optimistic by design, even when we know we shouldn’t be.